Field of the Invention
The present invention relates to a lubricating structure for a four-cycle engine with an enhanced lubrication feature for a cam of a camshaft, a tappet, which is pressed by this cam, and a tappet holder by which the tappet is held.
II. Description of the Related Art
A direct cast DOHC type four-cycle engine is structured, for example, so that a cam formed on a camshaft directly presses the tappet of an intake-exhaust valve. A plurality of cam journals are formed along with a cam on a camshaft and these cam journals are supported by cam bearings provided on the cylinder head. Generally, a pair of cams is formed adjacent to a cam journal at both ends.
The camshaft is a hollow shaft and its interior is used as an oil supply path. A journal path that branches off at a right angle away from this oil supply path opens on the peripheral surface of the cam journal, and oil pumped out through the oil supply path is supplied between the cam journal and the cam bearing to lubricate them. At the same time, excess oil that has overflowed from a gap between the cam journal and the cam bearing causes lubrication between the cam and the tappet and between the tappet and the tappet holder.
However in, for example, a vertical four-cycle engine that can be mounted on a outboard motor and whose crankshaft and camshaft are disposed vertically, a cam and a tappet disposed at a higher position than the uppermost cam journal tend to be hardly lubricated, and lubrication conditions for the uppermost cam, the tappet, and the periphery of the tappet holder gets worse, resulting in seizure or uneven wear.
In this case, there may be a possibility of providing an exclusive oil path communicating with a periphery of the uppermost cam, the tappet and the tappet holder to lubricate them intensively. However, the structure of the engine becomes more complex by providing the oil path and oil is discharged continuously from the oil path. Therefore, the oil pressure of the entire engine decreases easily and there is concern that problems will occur in other lubricated portions within the engine. Therefore, this alternative design is not desirable.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the advantages and purposes of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
The present invention was made in order to solve the above described exemplary problems. Hence, an exemplary objective is to provide a lubricating structure for a four-cycle engine that is simple, but enables oil to be supplied to cams that are in difficult locations to supply, and in the vicinity of the tappets and the tappet holders, without decreasing oil pressure and improving lubrication conditions to prevent seizure and uneven wear from occurring.
In order to achieve these exemplary objectives, the lubricating structure for a four-cycle engine related to the present invention comprises a camshaft having an oil supply path at the axial center thereof and formed with a cam adjacent to a cam journal for pressing a tappet, a journal path branched away from the oil supply path which opens into an opening on the outer peripheral surface of the cam journal so as to supply oil thereto and a cam bearing that supports this cam journal, and wherein an intermittent oil supply means which intermittently discharges some of the oil supplied to the cam bearing and the cam journal from the oil supply path intermittently through the journal path to the cam and the side of the tappet in line with the rotation of the camshaft.
Also, in the present invention relating to a lubricating structure for a four-cycle engine the intermittent oil supply means is preferably structured so that an oil groove is formed on the bearing surface of the cam bearing in alignment with the axial direction of the camshaft, and at least one end of this oil groove opens on an end face of the cam side of the cam bearing.
Furthermore, in the present invention relating to a lubricating structure for a four-cycle engine, the intermittent oil supply means is further structured so that an oil hole is formed for communicating between the bearing surface of the cam bearing and the end face of the cam side, and the axial direction of the opening of the oil hole on the bearing surface side coincides with the axial direction of the journal path that opens on the outer peripheral surface of the cam journal, and the axial direction of the oil hole is oriented to the cam side.
Moreover, in the present invention relating to a lubricating structure for a four-cycle engine, the intermittent oil supply means is still further structured so that a cylindrical tappet pressed by the cam is disposed adjacent to the bearing whereby the bearing surface of the cam bearing is formed with a wide portion and a narrow portion, the position in the axial direction in which the opening on the outer peripheral surface of the cam journal of the journal path is located where the rotational pathway of the journal path is limited to within the widest portion of the bearing surface and, the rotational pathway of the journal path is located outside the range of the narrowest portion of the bearing surface.
Furthermore, in the present invention relating to a lubricating structure for a four-cycle engine, the intermittent oil supply means is structured so that a cylindrical tappet pressed by the cam is located adjacent to the cam bearing and the bearing surface of the cam bearing is formed with a wide portion and a narrow portion, then an oil groove that extends in the axial direction of the camshaft is formed on the outer peripheral surface of the cam journal, and the positioning and length of the oil groove in the axial direction is disposed such that the rotational pathway of the entire oil groove is limited to within the range of the widest portion of the bearing surface and, moreover, one end of the oil groove is disposed at a location outside the narrowest portion of the bearing surface on the side of the tappet, and the journal path opens inside this oil groove.
It is to be understood that both the foregoing general description and the following detailed description are only exemplary, and are intended to provide further explanation of the invention as claimed.